**Question:** Sensitivity to local anaesthetics is greater in

A. peripheral nerves
B. central nervous system
C. individuals with low body weight
D. elderly individuals

**Correct Answer:** C. individuals with low body weight

**Core Concept:** Local anaesthetics are drugs used to temporarily block pain signals in the body by inhibiting voltage-gated sodium channels in nerve cells. These channels play a crucial role in the generation and conduction of electrical impulses, which is essential for neuronal communication and function.

**Why the Correct Answer is Right:** Individuals with low body weight generally have a higher concentration of drugs in their bloodstream relative to body weight. This means that a smaller dose of local anaesthetic will have a greater effect on these individuals, making them more sensitive to the drug.

**Why Each Wrong Option is Incorrect:**

A. Peripheral nerves are the primary targets of local anaesthetics, where they block the transmission of pain signals. However, the sensitivity of peripheral nerves to local anaesthetics is not the deciding factor in determining overall sensitivity.

B. The sensitivity to local anaesthetics does not depend on the central nervous system (CNS) directly. Although CNS can be affected by high doses of local anaesthetics, the question specifically focuses on peripheral sensitivity.

C. The statement that low body weight increases sensitivity to local anaesthetics is the correct answer. In contrast, high body weight will lead to a higher volume of distribution, reducing the drug concentration and potentially reducing sensitivity.

D. Elderly individuals may have altered pharmacokinetics and pharmacodynamics due to age-related changes. However, this option is less relevant compared to the correct answer of low body weight, as the question is about sensitivity to local anaesthetics, not age-related alterations in pharmacokinetics.

**Clinical Pearl:** Understanding the pharmacokinetics and pharmacodynamics of local anaesthetics is crucial when choosing the appropriate dose for patients. The concept of body surface area and body weight is essential in determining the optimal local anaesthetic dosage for different patients. In clinical practice, this concept is often used to prevent potential overdose or underdose of local anaesthetics, ensuring safe and effective pain management.